Enslaved active implantable medical devices (sometimes such pacing devices are known as rate responsive devices in the context that an applied cardiac pacing rate is adjusted according to the parameters collected) generally employ two different kinds of sensors, i.e. one sensor for the measurement of a corporal parameter predominantly physiologic in nature, and one sensor for the measurement of a corporal parameter predominantly physical in nature.
For purposes of illustration, a particular example of a minute-ventilation (VE) sensor will be used as the physiologic sensor, corresponding to a conventional practice. However, it should be understood that this example is not intended to limit the scope of the invention, and other types of sensors may equally be used to obtain a physiologic parameter other than minute ventilation, which devices provide a signal that is representative of the patient's metabolic needs (for example, a sensor that measures blood oxygen saturation) or hemodynamic status (for example, an intracardiac bioimpedance sensor). The term “sensor” should be understood to include the physical components that interface with the patient to collect the information underlying the patient parameter and the related electronic circuits, algorithms and logic that process the collected information to produce a parameter measurement.
Similarly, for purposes of illustration a particular example of an acceleration (G) sensor will be used as the physical parameter (activity), corresponding to a conventional practice. Here, too, other types of physical sensors can be considered, notably to detect the patient's movements. Generally, the physical (activity) sensor is characterized by having a shorter response time than the physiological sensor, in order to allow a very fast detection of short-duration activity, and to use that detected activity before a change in the patient's metabolic demand can be identified through a significant change of the collected physiological parameter, which varies more slowly.
European patent EP 0,750,920, and its counterpart U.S. Pat. No. 5,722,996, commonly assigned herewith to ELA Medical, describe such an active implantable medical device that is enslaved to two sensors, operating a selection of one or the other sensor as the control parameter so as to take into account only that which gives the more relevant signal at a given moment. European patent EP 0,919,255 and its counterpart U.S. Pat. No. 6,336,048, also commonly assigned herewith to ELA Medical, describe an enslavement that is based upon the use of a combination of the signals provided by these two sensors.
Many patients implanted with an active implantable medical device present a normal atrio-ventricular conduction (i.e., each atrial event is followed by an associated ventricular depolarization) and therefore have no standard indication for being implanted with a pacemaker. A multisite device is then indicated, so as to treat the indicated heart failure, in order to improve the general hemodynamic state of these patients, through permanent jointly pacing of right and left ventricles so that they can be resynchronized. Such therapy has often provided surprisingly effective results on patients suffering from Class III heart failure, that were not improved through the prior known, classical treatments. European patent EP-A-1,543,864 and its U.S. counterpart published patent application US 2005/0,131,471 (commonly assigned herewith to ELA Medical) describe such a multisite device.
The starting point of the present invention lies in the observation by the inventor that medical practitioners have no convenient tool that allows them, during routine visits, to immediately and objectively assess whether the applied therapy actually led to an expected improvement of the patient's exercise performance status. Therefore, there is a recognized need to have such a function implemented in such devices that permits the elaboration and memorization of the information relating to the evolution of the patient's clinical status between two routine visits to the medical practitioner, that is over a long period of time, for these visits are usually spaced several months apart.
An objective assessment of this evolution will notably allow the practitioner to determine whether multisite pacing is beneficial, and eventually to choose a programming that is more appropriate to the particular patient, or, for example, to be informed about the occurrence of important ventilation disorders, not diagnosed by the patient himself.
Heretofore, for the purpose of evaluating, for example, the effect of a particular programming on the patient's status between two routine visits, the practitioner could only rely on the facts and feelings reported by the patient—such information being subject to a strong subjectivity—or on clinical tests performed or prescribed—the latter information provided by such tests only reflecting the patient's status at the time of the tests, with no retrospective overview on the improvement or degradation of the patient's status between visits.
There also is an existing need for providing a synthetic and significant diagnostic aid that can be represented through a simple and clear symbolic form, i.e. a clear visual presentation, to the practitioner during routine visits.